Question 746597
Add their rates of filling
1st pipe: ( 1 tank filled ) / ( 4 hrs )
2nd pipe: ( 1 tank filled ) / ( 5 hrs )
3rd pipe: ( 1 tank filled ) / ( 6 hrs )
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{{{ 1/4 + 1/5 + 1/6 = 1/t }}}
Multiply both sides by {{{ 60t }}}
{{{ 15t + 12t + 10t = 60 }}}
{{{ 37t = 60 }}}
{{{ t = 1.622 }}} hrs
{{{ .622*60 = 37 }}}
All 3 pipes working together take 1 hr and 37 min